随机显示广告代码：
add_filter( 'the_content', 'prefix_insert_post_ads' );
function prefix_insert_post_ads($content){
  $pattern = "/<p>.*?</p>/";
  $paragraph_count = preg_match_all($pattern,$content); //计算文章的段落数量
  if($paragraph_count >= 8 && is_single()){ // 如果文章的段落数量少于 8 段，则不会插入文章段落广告
    $paragraph_count -=2;
    $insert_paragraph=rand(3,$paragraph_count);
    $ad_code = '<div>你的广告代码</div>';
    return prefix_insert_after_paragraph( $ad_code, $insert_paragraph, $content );
  }
  return $content;
}
// 插入广告所需的功能代码
function prefix_insert_after_paragraph( $insertion, $paragraph_id, $content ) {
  $closing_p = '</p>';
  $paragraphs = explode( $closing_p, $content );
  foreach ($paragraphs as $index => $paragraph) {
    if ( trim( $paragraph ) ) {
    $paragraphs[$index] .= $closing_p;
    }
    if ( $paragraph_id == $index + 1 ) {
      $paragraphs[$index] .= $insertion;
    }
  }
  return implode( '', $paragraphs );
}